Tetrasomy 9p due to an intrachromosomal triplication of 9p13-p22

Abstract

To date, approximately 30 patients have been described with a tetrasomy 9p, all being caused by the presence of an isochromosome 9p. We now report on a 3-year-old boy with a de novo intrachromosomal triplication of 9p13-p22, resulting in partial tetrasomy 9p. We compared his phenotype with cases of tetrasomy 9p caused by the presence of an extra isochromosome 9p. He has facial anomalies similar to those of cases of tetrasomy 9p, central nervous system abnormalities, and severe psychomotor retardation but no other major congenital anomalies. Fluorescence in situ hybridization with region-specific probes showed that the middle repeat of the triplicated part is inverted. Microsatellite analysis demonstrated an involvement of both paternal chromosome 9 homologues in the triplication. This is compatible with either unequal crossing over of three of the four chromatids in paternal meiosis I or with a double crossing over in meiosis I and II (or an early mitotic division).

Tandem triplication of chromosome 13q14 with inverted interstitial segment in a 4 year old girl

“…This type of triplication has so far been reported for the following chromosomal segments: 2q11.2-q21,7 2q37,25p14-p15.33,3 7p21.2-p21.3,49p13-p22,5 10q26,6 13q14 (present report), and 15q11-q13 120 21 It is interesting to note that in several cases an unequal distance between two FISH signals (the proximal and the middle versus the middle and the distal) indicated that either the middle segment was inverted or, less likely, the middle segment was in normal orientation, but the proximal and distal segments were inverted,1 4 6 probably, according to the illustrations, the cases of Rauch et al 2 and Harrison et al 3 and the present report.…”

Intrachromosomal triplications: molecular cytogenetic and clinical studies

“…The chromosome region 15q11q13 appears to be prone to triplication since it is involved in 50% of the reported cases ( Table 2) [1,3,13–24]. It is possible that the same hot spots involved in small inversion duplications and deletions of 15q11q13 [25] may also be involved in the triplications.…”

Prenatal diagnosis and findings of tetrasomy 9p

“…Non‐mosaic cases have a high incidence of mortality in the neonatal period based on prior reports . In the case reported by Verheij et al . of tetrasomy 9p due to an intrachromosomal triplication of 9p13‐p22, similarities existed between the patient and previously reported tetrasomy 9p patients (including psychomotor retardation, hydrocephalus, large fontanels, hypotonia, and similar facial anomalies).…”

“…Isochromosomes derived from chromosome 9 have been reported and can be grouped into three types: isochromosomes with a breakpoint at p10 with no portion of the long arm, isochromosomes with a small amount of the heterochromic region of 9q extending to 9q12 or 9q13, and isochromosomes with a large portion of the long arm of chromosome 9 extending to 9q21 or q22 . An unusual case of partial tetrasomy 9p caused by an intrachromosomal triplication of a part of chromosome 9p has also been reported . The karyotype was designated 46,XY,trp(9)(pter p13:p13 p22:p22®p13:p13qter), resulting in a tetrasomy of chromosome 9p13‐p22.…”